Which difficulty did the builders of the transcontinental railroad have to overcome?
a. building on the wet, marshy soil of the great plains
b. meeting the demands of skilled union workers
c. providing supplies to build tracks and support workers
d. bridging the grand canyon and rio grande river

C. providing supplies to build tracks and support workers

Explanation:

One of the main problems with building railroads is that you have large extensions of land that have nothing around in which the railroad is supposed to pass and you have no means to feed and to get supplies for workers and the construction of the Railroad, so one of the difficulties that the builders of the transcontinental railroad had to overcome was providing supplies to build the tracks and to support workers there.

i think you may have asked this twice, but i answered one of the